1. Field of the Invention
The present invention relates generally to blowout preventers forming a part of well drilling equipment, as used for example in the drilling for oil and gas. More particularly, this invention relates to a sealing element for a ram-type blowout preventer, wherein the seal element is compressible to accommodate a range of drill pipe sizes.
2. The Prior Art
During drilling for oil and gas, instances occur when the drill string must be sealed to prevent damage to the well and associated equipment. Various types of blowout preventer equipment have been used in the past to provide such a seal. For example, U.S. Pat. No. 3,736,982 discloses shear-type and ram-type blowout preventers; and U.S. Pat. No. 3,667,721 discloses a spherical-type blowout preventer.
Generally speaking, the ram-type blowout preventer is preferred in certain circumstances because of its longer life expectancy than the spherical-type blowout preventer. However, governmental restrictions now require that two ram-type blowout preventers must be used per pipe size. This becomes significant when drilling at greater depths, since tapered drill strings are employed using various sized pipes. Therefore, several of the prior types of blowout preventers are required in these circumstances, since the seal elements of those prior ram-type preventers can accommodate only one size of pipe.
The present invention is directed to a variable ram seal for a blowout preventer that can be used with various sized pipes, and thereby provide the advantages set forth later in this disclosure. One variable ram seal has already been marketed. However, that particular ram includes steel support elements molded into the rubber such that the support elements rotate inwardly much like the shutter elements in a camera. This type of movement is believed to create unnecessary degrees of stress in the seal element, which can potentially create wear for a relatively short life expectancy.